Deposition of high-purity silicon via high-surface area gas-solid interfaces and recovery via liquid phase

Abstract

Solid silicon is deposited onto electrically heated deposition plates by the reduction reaction of gaseous trichlorosilane and hydrogen which are mixed and pumped across the surfaces of the plates. The plates can have a number of high-surface area geometries such as concentric cylinders, spirals, or repeating S-shapes. Once the desired amount of silicon has been deposited, the deposition plates are heated to above the melting point of silicon causing the deposited silicon to slide off the plates in the form of a crust due to gravitational force. The plates are left coated with a thin film of liquid silicon which contains any impurities leached from the plates. This film is melted off separately from the main silicon crust to avoid contamination of the latter and the plates are then ready for the next deposition cycle.

The invention claimed is: 
     
       1. A method for producing high-purity silicon comprising the steps of:
 a. Creating one or more deposition plates each with one or more deposition surfaces which have a high surface area, which can be rapidly, homogenously, and simultaneously heated, and which will not contaminate high-purity silicon, 
 b. Having a geometry for said deposition plates such that the ratio of average deposition surface area to deposition reactor internal volume is increased, 
 c. Placing said deposition plates in a deposition reactor, 
 d. Flowing a deposition gas mixture into the deposition reactor to deposit silicon onto the deposition surfaces wherein the deposition gas mixture flows through the spaces between the deposition plates and the deposition surfaces are heated to a temperature that optimizes the deposition reaction of the deposition gas mixture, 
 e. After the desired amount of silicon has been deposited, further heating the deposition plates to above the melting point of silicon so as to create only a thin layer of liquefied silicon between the plate and the remaining solid crust of deposited silicon, 
 f. Sliding off the solid crust of deposited silicon from the deposition plates by applying a force such as gravitational force. 
 
     
     
       2. The method for producing high-purity silicon in  claim 1  wherein the deposition gas mixture includes one or more members of the group consisting of trichlorosilane, silicon tetrachloride, and other silanes. 
     
     
       3. The method for producing high-purity silicon in  claim 1  wherein the deposition plates are made from materials which will not contaminate high-purity silicon and which have the appropriate structural, electrical, and thermal characteristics, such as tungsten, silicon carbide, silicon nitride, graphite, and alloys and composites of these materials. 
     
     
       4. The method of producing high purity silicon in  claim 1  wherein the solid crust of deposited silicon is supported by a container such as a crucible and does not slide off the deposition plates once they have been heated to above the melting temperature of silicon. 
     
     
       5. The method for producing high-purity silicon in  claim 4  wherein the deposition plates completely melt the solid crust of deposited silicon and the container with the resulting liquid silicon is pulled away from the deposition plates in a controlled manner such that the liquid silicon directionally solidifies into an ingot of multicrystalline silicon.